The invention relates to a device for the detachable fastening of a steering wheel on a steering shaft.
The use of steering wheels provided with gas bags in automobiles requires new techniques for the installation of the steering wheel on the steering shaft, because the interior of the steering wheel is no longer accessible from above.
It is known for example from the DE 41 06 096, to provide the steering shaft with a groove and to provide the hub with a through-bore which intersects this groove, and in this through-bore to arrange a fastening means consisting of a bolt and a nut screwed onto this bolt, a part of the bolt and/or of the nut engaging into the groove of the steering shaft on tightening of the nut and bolt connection and in this way locking the hub and the steering shaft with each other. As also in the use of nuts screwed from above onto the steering shaft, the torques occurring during traveling are transferred via force-fitting serrations in the steering shaft and the hub.
In order to be able to separate the steering wheel from the steering shaft without difficulty, for example for changing the steering wheel or the gas bag module, it is necessary that the nut and bolt connection can be detached simply and reliably.
This is achieved in a device for the detachable fastening of a steering wheel on a steering shaft having an axis. The steering wheel has a hub provided with a through-bore arranged perpendicularly to the axis of the steering shaft and the through-bore intersects a groove arranged in the steering shaft. The device comprises a fastening means arranged in the through-bore. The fastening means has a bolt with a head and a shaft provided at least partially with an external thread and has a nut able to be screwed onto the shaft of the bolt. The nut is able to engage into the groove and the through-bore has two oppositely directed radial support surfaces arranged between the bolt head and the nut. One support surface is arranged on the bolt head side and the other support surface is arranged on the nut side. A spring element is provided which engages one of the bolt and the nut and exerts a force onto one of the bolt and the nut. The force tries to increase, i.e. aims for an increase of a distance between the bolt head and the nut. The fastening means consisting of bolt and nut forms a nut and bolt connection. On tightening of the nut and bolt connection, the spring element is compressed and pre-stressed. On detaching of the nut and bolt connection, the energy stored in the spring provides for the bolt head and nut to be pressed apart and for the nut to leave the engagement with the groove, so that the steering wheel can be simply removed from the steering shaft.
In a preferred embodiment of the invention, the spring element is arranged between the support surface on the nut side and the nut. In this way, it is ensured that on detachment of the nut and bolt connection the nut moves outwards to the end of the through-bore on the nut side and no longer engages into the groove of the steering shaft.
In a further preferred embodiment of the invention, the spring element is arranged between the support surface on the bolt head side and the bolt head. In this way, the bolt can be easily removed after the detachment of the nut and bolt connection.
It is necessary to secure the nut against rotation in the through-bore, in order to avoid a co-rotation of the nut with the bolt during the tightening movement or during the detachment of the connection.
Advantageously the end of the through-bore on the nut side is secured against the nut falling out, e.g. by caulking.